sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 6
Color: Brown, gray, or tan
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments; can date back billions of years.

Uses & applications

Historically used for stone tools and starting fires (striking steel); currently used in construction aggregate and as decorative landscaping stones.

Geological facts

Chert was a vital resource for prehistoric humans to create sharp-edged tools like arrowheads and knives because of its predictable conchoidal fracture patterns.

Field identification & locations

Look for a microcrystalline texture that produces sharp edges when broken; commonly found in limestone or chalk beds. Collectors should look for unique banding or color patterns.